Rectangular contact used as a low voltage fuse element

ABSTRACT

A repair fuse element and method of construction are disclosed that eliminate or substantially reduce the disadvantages and problems associated with prior fuse elements. In one embodiment, the fuse element is constructed with a rectangular-shaped contact. The contact is made long enough so that it makes contact at each end with a metal layer, but design rule spacing is still maintained between the connections with the metal layer. The overlapping areas between the rectangular contact and the metal layers are asymmetrical. Alternatively, these overlapping areas are smaller than the design rule overlap requirements. In a second embodiment, a fuse element is constructed with a plurality of rectangular-shaped contacts. As a result, a current value that is significantly lower than conventional fuse current values, can be used to melt such a contact or blow the fuse.

This application claims priority under 35 USC § 119(e)(1) of provisionalapplication numbers 60/322,190 filed Sep. 13, 2001.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the semiconductor processingfield and, in particular, to a low voltage fuse element and method offabrication.

BACKGROUND OF THE INVENTION

Certain semiconductor devices, such as dynamic random access memories(DRAMs) and static RAMs (SRAMs), are designed with redundant rows and/orcolumns of memory bits. The redundant rows and columns can be connectedinto a memory array to substitute for memory cells found defectiveduring the testing and inspection process. This connection can be madeby blowing selected fuses that are strategically located in the memoryarray and the redundant rows and columns. Typically, these fuses aremade of polysilicon formed on a field oxide layer simultaneously with agate electrode. Alternatively, these fuses can be made of a metalmaterial.

A significant problem experienced with conventional polysilicon fuses isthat they have relatively high inherent and parasitic resistances. Onthe other hand, the current required to blow such a polysilicon fuse isrelatively low. A significant problem experienced with conventionalmetal fuses is that they require exceedingly high currents to make themblow. However, the inherent resistance of such metal fuses is relativelylow.

SUMMARY OF THE INVENTION

Accordingly, there is a need for a fuse element with low inherentresistance, which also requires a low amount of current to melt the fuseelement and make it blow.

In accordance with the present invention, a fuse element and method ofconstruction are provided that eliminate or substantially reduce thedisadvantages and problems associated with prior fuse elements.

In one embodiment of the present invention, a fuse element isconstructed with a rectangular-shaped contact. The contact is made longenough so that it makes contact at each end with a metal layer, butdesign rule spacing is still maintained between the connections with themetal layer. In this embodiment, a polysilicon plate under the fuseelement is primarily to land the contacts and does not carry any of thefusing current. In one aspect, the overlapping areas between therectangular contact and the metal layers are selected to beasymmetrical. Alternatively, in another aspect, one or more of theseoverlapping areas is selected to be smaller than the design rule overlaprequirements.

In a second embodiment of the present invention, a fuse element isconstructed with a plurality of rectangular-shaped contacts. In thiscase, the overlapping areas of the metal layer and contacts are selectedto be asymmetrical. In this embodiment, the polysilicon supports thefusing element, but is not the fusing element.

An important technical advantage of the present invention is that a fuseelement is provided which has significantly lower inherent resistanceand parasitic resistance than prior polysilicon fuses.

Another important technical advantage of the present invention is that afuse element is provided which requires a significantly lower amount ofcurrent to blow than prior metal fuses.

Still another important technical advantage of the present invention isthat a fuse element is provided which requires a significantly lowerblow voltage than that used for prior fuses.

Yet another important technical advantage of the present invention isthat a fuse element is provided with a small overlap area between acontact and a metal layer, which can generate very high interfacialcurrent densities in a relatively compact layout.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following descriptions, takenin conjunction with the accompanying drawings, in which:

FIG. 1A is a cross-sectional view of a fuse element constructed inaccordance with an embodiment of the present invention;

FIG. 1B is a perspective view of the fuse element shown in FIG. 1A;

FIG. 2A is a cross-sectional view of a fuse element constructed inaccordance with a second embodiment of the present invention; and

FIG. 2B is a perspective view of the fuse element shown in FIG. 2A.

DETAILED DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention and its advantagesare best understood by referring to FIGS. 1A-2B of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1A is a cross-sectional view of a fuse element constructed inaccordance with an embodiment of the present invention. FIG. 1B is aperspective view of the fuse element shown in FIG. 1A. Referring toFIGS. 1A and 1B, a fuse element 10 is shown. For example, fuse element10 can be strategically located in a DRAM or SRAM memory array and/or inredundant columns and rows. As such, fuse element 10 can be located inany appropriate semiconductor device that incorporates electrical fusesfor memory or circuitry repair.

Fuse element 10 includes a substantially rectangular-shaped contact 12.For this exemplary embodiment, the contact 12 is formed on a polysiliconlayer or landing pad 14. The contact 12 is formed by filling the contactarea with tungsten. A lead wire (not shown) connected to the contact 12can be copper with a tantalum nitride liner. The lead wire can carry acurrent used to melt or blow the fuse.

A first metal line 16 and second metal line 18 of a metal layer, MET1,each overlay a respective end of the contact 12. For example, the metallayer, MET1, can form a first layer of a multi-level metal stack in amulti-metal level semiconductor device. Typically, such a stack caninclude a plurality of levels of metal and inter-level oxide ordielectric layers.

Referring to FIG. 1A, for this exemplary embodiment, the dimensions ofthe rectangular contact surface 12(a) (facing upwards in FIG. 1B) ofcontact 12 are 0.15 μm by 0.525 μm. It is to be understood that thethickness dimension of the contact 12 (distance between MET-1 layer andpolysilicon layer) is not significantly related to the function of thepresent invention and can be determined by conventional design rules.Preferably, the minimum distance or spacing 15 between the first metalline 16 and the second metal line 18 of the metal layer, MET1, is 0.175μm. However, for this embodiment, this distance or spacing 15 betweenthe metal lines 16, 18 is selected to be 0.365 μm.

According to design rules for the fuse element 10 configuration shown inFIGS. 1A and 1B, each of the lengths 11 and 13 by which the respectivemetal lines 16 and 18 overlap the contact surface 12(a) is 0.05 μm.Preferably, however, for this embodiment, the overlap dimensions 11 and13 are each selected to be 0.08 μm long. Using this overlap value ofapproximately 0.08 μm ensures that each of the overlapping areas islarge enough so that an open contact is not formed (e.g., at T0).

Preferably, the minimum thickness of the metal layer, MET1, is 2,500Angstroms. As such, the J_(rms) limit for the metal layer, MET1, is2.5E6 A/cm². If the metal line (16 or 18) to contact surface 12(a)overlap is 0.05 μm, the width 19 of the metal layer, MT1, is 0.25 μm.Moreover, the average current, I_(rms), of the metal layer, MT1, is 1.53mA. Thus, the current density at a metal line 16, 18 to contact 12overlap is 12.75E6 A/cm², 5.1×width of the lead (not shown). The widthof the lead can be increased in order to increase the I_(rms) value forthe metal layer, MT1.

In operation, the fuse element 10 can be used, for example, as anelectrically programmable fuse. The contact 12 can be connected to afloating polysilicon element of a memory array and/or redundant rows andcolumns. In order to blow the fuse 10, a current is conveyed through thebody of the contact 12 between the two MET1 lines 16, 18. If the metalline 16, 18 to contact 12 overlaps are selected to be asymmetrical(e.g., the overlap of metal line 16 to contact 12 is smaller than theoverlap of metal line 18 to contact 12, or vice versa), then a currentvalue which is significantly lower than conventional fuse currentvalues, can be used to melt the MET1-CONT interface (16/12) and blow thefuse. Alternatively, if either of the metal line 16, 18 to contact 12overlap dimensions is selected to be smaller than the design ruleoverlap dimension for such a fuse element configuration (e.g., theoverlap of metal line 16 to contact 12 is smaller than the design rulefor a metal line to contact overlap), then a current value which issignificantly lower than conventional fuse current values, can be usedto melt the MET1-CONT interface (16/12) and blow the fuse. Consequently,a significant additional advantage of the present invention is that alow voltage supply can be used to melt or blow such a fuse.

FIG. 2A is a cross-sectional view of a fuse element constructed inaccordance with a second embodiment of the present invention. FIG. 2B isa perspective view of the fuse element shown in FIG. 2A. Referring toFIGS. 2A and 2B, a fuse element 20 is shown. Fuse element 20 includes aplurality of substantially rectangular-shaped contacts 22(a) and 22(b).For this exemplary embodiment, the contacts 22(a) and 22(b) are formedon a polysilicon layer or landing pad 24. The contacts 22(a) and 22(b)can be formed by filling the contact areas with tungsten. A lead wire(not shown) connected to a contact 22(a) and/or 22(b) can be copper witha tantalum nitride liner. The lead wire can carry a current used to meltor blow the fuse.

A first metal line 26 and second metal line 28 of a metal layer, MET1,each overlay a surface of a respective contact 22(a) and 22(b).Preferably, for this embodiment, the overlap dimensions 21 and 23 areeach selected to be 0.08 μm. Using this overlap value of approximately0.08 μm ensures that each of the overlapping areas is large enough sothat an open contact is not formed (e.g., at T0). The width of thecontact 22(a) can be 0.08 μm, because the contact surface of contact22(a) is substantially square. The width of the contact 22(b) can be0.15 μm, which is similar to the width of contact 12 shown in FIGS. 1Aand 1B.

Preferably, the minimum thickness of the metal layer, MET1, is 2,500Angstroms. As such, the J_(rms) limit for the metal layer, MET1, is2.5E6 A/cm². If the metal line 26 to contact surface 22(a) overlap is0.05 μm, the width 29 of the metal layer, MT1, is 0.25 μm. Moreover, theaverage current, I_(rms), of the metal layer, MT1, is 1.53 mA. Thus, thecurrent density at the metal line 26 to contact 22(a) overlap is 12.75E6A/cm², 5.1×width of the lead (not shown). As such, the width of the leadcan be increased in order to increase the I_(rms) value for the metallayer, MT1. The operation of the second embodiment is essentiallysimilar to that of the first embodiment described above. However, forthe second embodiment, since the overlapping surfaces of the metal lines26, 28 to the contacts 22(a), 22(b), respectively, are asymmetrical,then a current value which is significantly lower than conventional fusecurrent values, can be used to melt the MET1-CONT interface (26/22(a))and blow the fuse.

Although a preferred embodiment of the method and apparatus of thepresent invention has been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it will be understoodthat the invention is not limited to the embodiment disclosed, but iscapable of numerous rearrangements, modifications and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

What is claimed is:
 1. A fuse element for a semiconductor device,comprising: at least one substantially rectangular contact; apolysilicon layer formed in said semiconductor device, a first surfaceof said at least one substantially rectangular contact formed on asurface of said polysilicon layer; and a plurality of metal lines formedfrom at least one metal layer in said semiconductor device, each line ofsaid plurality of metal lines formed to overlap a respective area of asecond surface of said at least one substantially rectangular contact.2. The fuse element of claim 1, wherein said plurality of metal linescomprises two metal lines, and whereby a first metal line of said twometal lines is formed to overlap a first area of said second surface ofsaid at least one substantially rectangular contact, and a second metalline of said two metal lines is formed to overlap a second area of saidsecond surface of said at least one substantially rectangular contact,said first area being smaller than said second area.
 3. The fuse elementof claim 1, wherein said plurality of metal lines comprises two metallines, and whereby a first metal line of said two metal lines is formedto overlap a first portion of said second surface of said at least onesubstantially rectangular contact by a first predetermined distance, anda second metal line of said two metal lines is formed to overlap asecond portion of said second surface of said at least one substantiallyrectangular contact by a second predetermined distance.
 4. The fuseelement of claim 3, wherein said first predetermined distance is lessthan said second predetermined distance.
 5. The fuse element of claim 3,wherein at least one distance of said first distance and said seconddistance is approximately 0.08 μm.
 6. The fuse element of claim 1,wherein said at least one substantially rectangular contact comprises atungsten material.
 7. The fuse element of claim 1, wherein said at leastone substantially rectangular contact further comprises a first contactand a second contact.
 8. The fuse element of claim 7, wherein saidplurality of metal lines comprises two metal lines, and whereby a firstmetal line of said two metal lines is formed to overlap a surface areaof said first contact, and a second metal line of said two metal linesis formed to overlap a surface area of said second contact, said surfacearea of said first contact being smaller than said surface area of saidsecond contact.